On Thu, 22 Jun 1995 23:44:47 -0400 you wrote:
GM>The panderichthyids don't have to do anything to advance this
>situation. The Acanthostega, advances the case quite nicely. It
>essentially has a half evolved leg! A glance at figure 2 of Coates
>and Clack (1990, p. 68) shows an amazing similarity of its humerus,
>radius and ulna and that of the fish fin of Eusthenopteron
I haven't got these pictures before me, and I await Ashby's (and Kurt
Wise's) reply. No one denies there are "similarities" between fish
and amphibia. I have got a picture of the Rhipidistian Fish
Eusthenopteron's skeleton compared with Ichthyostega, one of the
earliest amphibians. (Denton M., "Evolution: A Theory in
Crisis",1985, Burnett Books, p167). It seems clear that an enormous
difference exists between fish and amphibia.
GM>Ahlberg states: (1991, p. 298)
>"Note that the forelimb of Acanthostega is more fish-like than the hindlimb
>and could probably not be brought into a weight-bearing position."
>
GM>Coates and Clack (1990, p. 67) state,
>"In Acanthostega the terminal radial and ulnal condyles, and the lack of an
>olecranon process on the ulna, suggest that the forelimb could never have
>flexed from the elbow to lie in a fully load-bearing posture, and thei it was
>probably held horizontally."
>
GM>This is not a fully functional terrestrial leg! It makes one
>wonder about statements like
Indeed. Is it a "leg" at all?
GM>"There are no true transitional forms (that is, in the sense of
forms containing incipient, developing or transitional structures -
such as half-scales/half feathers, or half-legs/half wings) anywhere
among all the billions of known fossil forms." (Morris and Parker,
1987, p. 11)
Still true! There are no "half-scales/half feathers, or half-legs/half
wings".
GM>or
>"Not a single transitional form has ever been found showing an
intermediat stage between the fin of the crossopterygian and the foot
of the ichthyostegid." (Gish, 1989, p. 79)
Still possibly true. This fin doesn't seem to be a "foot"?
GM>I would suggest that Acanthostega with its not quite functional leg
>which must have been held horizontally, is a good candidate. (Coates
>and Clack, 1990, p. 67 at bottom)
Is it indeed a "leg"?
The point is that even if a half-fin / half-leg is eventually found,
it is clearly incredibly rare. There must surely have been billions of
these transitional structures (eg. fin-leg, arm-wing, scale-feather),
if naturalistic evolution is true. Only finding one or two would not
confirm the theory. It would suggest a more rapid transition than
purely naturalistic theories of evolution can allow.
Besides, while a single half-fin / half-leg might be the fatal to Fiat
Creationism (the quotes were from Creation-Scientists), their extreme
rarity could be good evidence for a modified Progressive Creation
model.
>Ashby Camp wrote:
AC>In contrast, the earliest land vertebrates (for which there
>are skeletal remains, i.e., _Ichthyostega_, _Acanthostega_, and
>_Tulerpeton_) "had short but massive limbs of the basic pattern of
>subsequent tetrapods" (Robert L. Carroll, "The Primary Radiation of
>Terrestrial Vertebrates," _Annual Review of Earth Planet Science_
>[1992] 20:47). These differences are so significant that Dr.
>Carroll states that "no fossils are known that can be considered
>intermediate between these clearly aquatic [osteolepiform] fish and
>genera that are unequivocally classified as terrestrial verte-
>brates" (_Ibid_., 45). <
I'm glad Ashby posted this. One would never have known it from
your description, Glenn! <g>
GM>These types of statements which are always quoted seem to indicate
>that the amphibian leg popped into existence with the modern
>morphology. This is not the case. Tetrapods today are based upon a
>5-digit form. The earliest tetrapods were polydactylous.
>Acanthostega had 8 digits on fore and back limbs. Ichtyostega had 7
>on the hind limb. Tulerpeton had six digits on >both fore and hind
>leg. (Ahlberg and Milner, 1994, p. 509).
The point is that you are claiming that Acanthostega was an
intermediate between fish and amphibia, but Carroll says "no fossils
are known that can be considered intermediate between these...fish and
..terrestrial vertebrates" (including Acanthostega).
GM>They state, "However, it now appears that neither the pentadactyl
>condition nor the canonical wrist pattern is primitive for tetrapods,
>which invalidates such earlier theories substantially if not
>completely." p. 509
GM>Thus the earliest tetrapods do not have wrists and legs like ours.
>If the modern tetrapod form is fully evolved, then they are half
>evolved.
GM>While Ashby does not like the Panderichthyids as an intermediate
>form, consider this,
>"Mobility between the front and back of the skull table is absent in
>all land vertebrates, and in fact is absent in one family of
>rhipidistian fish, the Panderichthyidae." (Carroll, 1992, p. 51)
>This is one more possible transitional feature.
It should be pointed out that there are two levels to evolution.
There is the morphological level and the mechanism level. Even if
it is shown at a morphological that amphibia descended from fish, or
land mammals from whales, this says nothing about the mechanism.
Evolutionists try to claim all the credit that finding possible
transitional forms confirms their theory, when it doesn't necessarily.
If God created progressively, the same evidence would support PC. To
claim it as evidence for naturalistic macro-evolution, evolutionists
would need to demonstrate a plausible Darwinist mechanism that would
bring about the change.
Darwinists claim that a fish developed legs from fins millions of
years before they were able to use them. Moreover, the fish also had
to develop a pelvis and shoulder for the legs to anchor to. Indeed
these structures would have to develop in parallel to be any use.
Darwinists cannot claim any development to meet a need. That would be
Lamarkism. The only mechanism they can claim is of random mutations
which were advantageous in a changing environment and hence
cumulatively naturally selected. That is, the incipient legs and
hip/shoulders enabled
the possessors at each stage to produce more offspring than their
fellow
fish which did not have these incipient features.
In other words, naturalistic macro-evolutionists would need to show in
a scientifically rigorous way that:
1. Genetic mutations can spontaneously produce major new structures
such a pelvis in a fish, even where there is no apparent homologue.
Examples would need to be documented or at least theoretically worked
out in terms of genetic theory. In particular, evolutionists should
specify whether it was by one massive macromutation or a series of
many
micro-mutations.
2. This new pelvic structure would confer a selective advantage on the
possessor of the mutation gene(s) over other members of the same
species, such that it and its desendants would produce more offspring
than its fellows. Evolutionists would need to specify clearly and
rigorously
what this selective advantage was.
3. Further mutations would occur *to this particular species* to
produce a shoulder as well as front and rear legs. If it is claimed
the
legs came first, then substitute these terms. At every stage
these incipient structures would need to confer selective advantages
on the possessors of these mutated genes. Again these selective
advantages would need to be clearly specified.
4. Evolutionists would need to rigorously explain why the existing
non-mutated desendants (eg. Latimeria) of the alleged ancestral
species
not only survived, but did for 200 million years, right down to the
present!
5. Finally evolutionists would need to rigorously explain why this
process only occurred once and is not ocurring now. In particular, if
incipient feet were a selective advantage over fins, and the mutations
that produced it were random (and in fact ocurred at least twice in
the species in question), why haven't they occurred repeatedly in
other fish species and been naturally selected in the same?
If evolutionists cannot rigorously explain these mechanisms in a
plausible and rigorous way in terms of basic neo-Darwinist theory,
then it
seems open to Progressive Creationists to maintain that they ocurred
through divine planning and direct intervention at strategic points.
God bless.
Stephen